Fuel cells produce electricity from chemical reactions. The chemical reactions typically react a fuel, such as hydrogen, and air/oxygen as reactants, and produce water vapor as a primary by-product. The hydrogen can be provided directly, in the form of hydrogen gas or liquid, or can be produced from other materials, such as hydrocarbon liquids or gasses. Fuel cell assemblies may include one or more fuel cells in a fuel cell housing that is coupled with a fuel canister containing the hydrogen and/or hydrocarbons. Fuel cell housings that are portable coupled with fuel canisters that are portable, replaceable, and/or refillable, compete with batteries as a preferred electricity source to power a wide array of portable consumer electronics products, such as cell phones and personal digital assistants. The competitiveness of these fuel cell assemblies when compared to batteries depends on a number of factors, including their size, efficiency, and reliability.
Providing hydrogen directly to fuel cell assemblies is typically not suitable for portable fuel cells. Hydrogen gas has a low energy density, and thus large volumes of hydrogen gas may be needed in order to provide a sufficient amount of energy to an electronic product. Liquid hydrogen typically must be stored at low temperatures and high pressure, making its storage difficult. Thus, hydrocarbon fuel sources are typically preferred for portable fuel cells.
However, hydrocarbon fuel sources are not typically suitable for direct use with fuel cells. More particularly, hydrocarbons, when used directly with fuel cells, leave carbon deposits and/or soot on the fuel cells. This can reduce the efficiency of the fuel cells and in some cases render them inoperable. For instance, fuel cell electrodes typically include pores for allowing gas to flow through to contact and react with electrolyte membranes, as will be discussed below. Carbon deposits on the fuel cells, however, may block the pores in the electrodes. The carbon deposits within the pores may also provide electrical short-circuit paths between the electrodes, thereby eliminating voltage gain of the fuel cell.
Hydrocarbon fuel also produces carbon monoxide, which bonds to active sites on the electrolyte membrane, resulting in carbon monoxide poisoning of the electrode and reducing fuel cell performance. The carbon monoxide must be cleaned off the membrane, for example with oxygen.
Thus, hydrocarbon fuels are typically reformed to produce hydrogen gas for fuel cells. However, many existing fuel cells that include hydrocarbon reformers are not suitable for portable use. More particularly, there is a need in existing systems and methods for portable fuel cells that provide better heat insulation to maintain the operating temperature of the fuel cell and to protect an end-user. There is also a need for smaller insulation size, to allow for decreased fuel cell size. Moreover, there is a need for systems and methods that have improved thermal management so that heat can be routed and shared between fuel cell components to allow the components to operate at high efficiencies. There is also a need for systems that use multiple reformers, and it is desired that the multiple reformers are maintained at particular temperatures that improve their efficiencies. Finally, it is desired that these components are housed in a portable structure suitable for use in portable electronics applications.